[pgpool-general: 441] Re: strange load balancing issue in Solaris
Tatsuo Ishii
ishii at postgresql.org
Thu May 10 11:45:44 JST 2012
Good. Fix committed in master/V3_1_STABLE/V3_0_STABLE.
--
Tatsuo Ishii
SRA OSS, Inc. Japan
English: http://www.sraoss.co.jp/index_en.php
Japanese: http://www.sraoss.co.jp
> It's working.
>
> Regards,
> Aravinth
>
>
> On Wed, May 9, 2012 at 5:26 PM, Tatsuo Ishii <ishii at postgresql.org> wrote:
>
>> Thanks for the hint. Attached is a patch trying to fix the
>> problem. Can you please try it?
>> --
>> Tatsuo Ishii
>> SRA OSS, Inc. Japan
>> English: http://www.sraoss.co.jp/index_en.php
>> Japanese: http://www.sraoss.co.jp
>>
>> > Yes the issue is with random() function.
>> >
>> > Looks like I have solved the problem by using rand.
>> >
>> > Regards,
>> > Aravinth
>> >
>> >
>> > On Wed, May 9, 2012 at 4:02 PM, Tatsuo Ishii <ishii at postgresql.org>
>> wrote:
>> >
>> >> Thanks. Apparently random() of Solaris could return value beyond
>> >> RAND_MAX! It's easy to fix the problem, but I would like to do it with
>> >> respcet to portability. Any idea?
>> >> --
>> >> Tatsuo Ishii
>> >> SRA OSS, Inc. Japan
>> >> English: http://www.sraoss.co.jp/index_en.php
>> >> Japanese: http://www.sraoss.co.jp
>> >>
>> >> >>From Solaris 10 (x86) man page:
>> >> >
>> >> >
>> >> > SYNOPSIS
>> >> > #include <stdlib.h>
>> >> >
>> >> > long random(void);
>> >> >
>> >> > void srandom(unsigned int seed);
>> >> >
>> >> > char *initstate(unsigned int seed, char *state, size_t
>> >> > size);
>> >> >
>> >> > char *setstate(const char *state);
>> >> >
>> >> > DESCRIPTION
>> >> > The random() function uses a nonlinear additive feedback
>> >> > random-number generator employing a default state array size
>> >> > of 31 long integers to return successive pseudo-random
>> >> > numbers in the range from 0 to 2**31 -1. The period of this
>> >> > random-number generator is approximately 16 x (2 **31 -1).
>> >> > The size of the state array determines the period of the
>> >> > random-number generator. Increasing the state array size
>> >> > increases the period.
>> >> >
>> >> > The srandom() function initializes the current state array
>> >> > using the value of seed.
>> >> >
>> >> >
>> >> > (...)
>> >> >
>> >> >
>> >> >
>> >> > Regards,
>> >> > Rafal
>> >> >
>> >> >
>> >> >
>> >> > -----Original Message-----
>> >> > From: pgpool-general-bounces at pgpool.net [mailto:
>> >> pgpool-general-bounces at pgpool.net] On Behalf Of Tatsuo Ishii
>> >> > Sent: Wednesday, May 09, 2012 11:44 AM
>> >> > To: caravinth at gmail.com
>> >> > Cc: pgpool-general at pgpool.net
>> >> > Subject: [pgpool-general: 431] Re: strange load balancing issue in
>> >> Solaris
>> >> >
>> >> > Thanks.
>> >> >
>> >> > 2012-05-09 14:31:48 LOG: pid 22459: r: 268356063.000000
>> total_weight:
>> >> 32767.000000
>> >> >
>> >> > This is really weird. Here pgpool caculate this:
>> >> >
>> >> > r = (((double)random())/RAND_MAX) * total_weight;
>> >> >
>> >> > Total weight is same as RAND_MAX. It seems your random() returns
>> >> > bigger than RAND_MAX, which does not make sense because man page of
>> >> > random(3) on my Linux says:
>> >> >
>> >> > The random() function uses a non-linear additive feedback
>> >> random number
>> >> > generator employing a default table of size 31 long integers
>> to
>> >> return
>> >> > successive pseudo-random numbers in the range from 0 to
>> RAND_MAX.
>> >> The
>> >> > period of this random number generator is very large,
>> >> approximately
>> >> > 16 * ((2^31) - 1).
>> >> >
>> >> > What does your man page for random() say on your system?
>> >> > --
>> >> > Tatsuo Ishii
>> >> > SRA OSS, Inc. Japan
>> >> > English: http://www.sraoss.co.jp/index_en.php
>> >> > Japanese: http://www.sraoss.co.jp
>> >> >
>> >> >> Sorry . I missed it.
>> >> >>
>> >> >> Here is the log file.
>> >> >>
>> >> >> --Aravinth
>> >> >>
>> >> >>
>> >> >> On Wed, May 9, 2012 at 2:07 PM, Tatsuo Ishii <ishii at postgresql.org>
>> >> wrote:
>> >> >>
>> >> >>> > The code you have sent is same in child.c.
>> >> >>>
>> >> >>> No.
>> >> >>>
>> >> >>> pool_log("r: %f total_weight: %f", r, total_weight);
>> >> >>>
>> >> >>> You need to add the line above to get usefull information.
>> >> >>> --
>> >> >>> Tatsuo Ishii
>> >> >>> SRA OSS, Inc. Japan
>> >> >>> English: http://www.sraoss.co.jp/index_en.php
>> >> >>> Japanese: http://www.sraoss.co.jp
>> >> >>>
>> >> >>>
>> >> >>> > I have attached the log file. Please check
>> >> >>> >
>> >> >>> >
>> >> >>> > --Aravinth
>> >> >>> >
>> >> >>> >
>> >> >>> > On Tue, May 8, 2012 at 6:20 AM, Tatsuo Ishii <
>> ishii at postgresql.org>
>> >> >>> wrote:
>> >> >>> >
>> >> >>> >> I suspect there's some portablity issue with load balance code.
>> The
>> >> >>> >> actual source code is in select_load_balancing_nodechild.c).
>> >> >>> >> Please modify source code and connect to pgpool by using psql.
>> >> >>> >> Please send the log output.
>> >> >>> >> --
>> >> >>> >> Tatsuo Ishii
>> >> >>> >> SRA OSS, Inc. Japan
>> >> >>> >> English: http://www.sraoss.co.jp/index_en.php
>> >> >>> >> Japanese: http://www.sraoss.co.jp
>> >> >>> >>
>> >> >>> >> int select_load_balancing_node(void)
>> >> >>> >> {
>> >> >>> >> int selected_slot;
>> >> >>> >> double total_weight,r;
>> >> >>> >> int i;
>> >> >>> >>
>> >> >>> >> /* choose a backend in random manner with weight */
>> >> >>> >> selected_slot = MASTER_NODE_ID;
>> >> >>> >> total_weight = 0.0;
>> >> >>> >>
>> >> >>> >> for (i=0;i<NUM_BACKENDS;i++)
>> >> >>> >> {
>> >> >>> >> if (VALID_BACKEND(i))
>> >> >>> >> {
>> >> >>> >> total_weight +=
>> >> BACKEND_INFO(i).backend_weight;
>> >> >>> >> }
>> >> >>> >> }
>> >> >>> >> r = (((double)random())/RAND_MAX) * total_weight;
>> >> >>> >> pool_log("r: %f total_weight: %f", r, total_weight);
>> >> >>> <--
>> >> >>> >> add this
>> >> >>> >>
>> >> >>> >> total_weight = 0.0;
>> >> >>> >> for (i=0;i<NUM_BACKENDS;i++)
>> >> >>> >> {
>> >> >>> >> if (VALID_BACKEND(i) &&
>> >> BACKEND_INFO(i).backend_weight >
>> >> >>> >> 0.0)
>> >> >>> >> {
>> >> >>> >> if(r >= total_weight)
>> >> >>> >> selected_slot = i;
>> >> >>> >> else
>> >> >>> >> break;
>> >> >>> >> total_weight +=
>> >> BACKEND_INFO(i).backend_weight;
>> >> >>> >> }
>> >> >>> >> }
>> >> >>> >>
>> >> >>> >> pool_debug("select_load_balancing_node: selected backend
>> id
>> >> is
>> >> >>> %d",
>> >> >>> >> selected_slot);
>> >> >>> >> return selected_slot;
>> >> >>> >> }
>> >> >>> >>
>> >> >>> >>
>> >> >>> >> > Hi Tatsuo, Thanks for the reply.
>> >> >>> >> >
>> >> >>> >> > The normalized weights are 0.5 for both nodes and the selected
>> >> node is
>> >> >>> >> always the same node. I hope then it's srandom().
>> >> >>> >> >
>> >> >>> >> >
>> >> >>> >> > Any idea to solve this srandom issue
>> >> >>> >> >
>> >> >>> >> >
>> >> >>> >> > Thanks and Regards,
>> >> >>> >> > Aravinth
>> >> >>> >> >
>> >> >>> >> >
>> >> >>> >> > ________________________________
>> >> >>> >> > From: Tatsuo Ishii <ishii at postgresql.org>
>> >> >>> >> > To: aravinth at mafiree.com
>> >> >>> >> > Cc: pgpool-general at pgpool.net
>> >> >>> >> > Sent: Tuesday, May 1, 2012 4:41 AM
>> >> >>> >> > Subject: Re: [pgpool-general: 396] strange load balancing
>> issue in
>> >> >>> >> Solaris
>> >> >>> >> >
>> >> >>> >> > First of all please check "normalized" weights are as you
>> >> expected.
>> >> >>> >> > Run "show pool_status;" and see "backend_weight0",
>> >> "backend_weight1"
>> >> >>> >> > section. You see a floating point numbers, which are the
>> >> normalized
>> >> >>> >> > weight between 0.0 and 1.0. If you see both are 0.5, primary
>> and
>> >> >>> >> > standby are given same weight.
>> >> >>> >> >
>> >> >>> >> > If they are ok, I suspect srandom() function behavior is
>> different
>> >> >>> >> > from other platforms. Pgpool-II chooses the load balance node
>> by
>> >> using
>> >> >>> >> > srandom(). select_load_balancing_node() is the function which
>> is
>> >> >>> >> > responsible for selecting the load balance node. If you run
>> >> pgpool-II
>> >> >>> >> > with -d (debug) option, you will see following in the log:
>> >> >>> >> >
>> >> >>> >> > pool_debug("select_load_balancing_node: selected backend
>> id is
>> >> >>> %d",
>> >> >>> >> selected_slot);
>> >> >>> >> >
>> >> >>> >> > If backend_weight in show pool_status are fine but the line
>> above
>> >> >>> >> > always shows same number, it is the sign that we have problem
>> with
>> >> >>> >> > srandom().
>> >> >>> >> > --
>> >> >>> >> > Tatsuo Ishii
>> >> >>> >> > SRA OSS, Inc. Japan
>> >> >>> >> > English: http://www.sraoss.co.jp/index_en.php
>> >> >>> >> > Japanese: http://www.sraoss.co.jp
>> >> >>> >> >
>> >> >>> >> >> Hi All,
>> >> >>> >> >>
>> >> >>> >> >> I am facing a strange issue in load balancing with replication
>> >> mode
>> >> >>> set
>> >> >>> >> to
>> >> >>> >> >> true in Solaris. Load balancing algorithm always select the
>> same
>> >> node
>> >> >>> >> >> whatever may be the backend weight
>> >> >>> >> >>
>> >> >>> >> >> Here is the scenario.
>> >> >>> >> >>
>> >> >>> >> >> I have a pgpool installed installed in 1 server
>> >> >>> >> >> 2 postgres nodes in other 2 servers
>> >> >>> >> >> replication mode set to true and load balancing set to true
>> >> >>> >> >> backend weight of the 2 nodes is 1.
>> >> >>> >> >>
>> >> >>> >> >> When I fire the queries manuall using different connections or
>> >> using
>> >> >>> >> >> pgbench all the queries hit the same node. Load balancing
>> >> algorithm
>> >> >>> >> always
>> >> >>> >> >> select the same node.
>> >> >>> >> >> No effect in changing the backend weight. Only when I set
>> backend
>> >> >>> >> weight to
>> >> >>> >> >> 0 hits go to the other server.
>> >> >>> >> >>
>> >> >>> >> >>
>> >> >>> >> >> I face this issue only in solaris. The same setup in other
>> >> servers (
>> >> >>> >> centos
>> >> >>> >> >> ,RHEL, ubunt etc) does the load balancing perfectly.
>> >> >>> >> >>
>> >> >>> >> >> Also tries various postgres versions and pgpool version with
>> same
>> >> >>> >> result.
>> >> >>> >> >> But every version runs fine in other servers.
>> >> >>> >> >>
>> >> >>> >> >> Has anyone faced this issue?
>> >> >>> >> >>
>> >> >>> >> >> Any information would highly helpful.
>> >> >>> >> >>
>> >> >>> >> >> Regards,
>> >> >>> >> >> Aravinth
>> >> >>> >> _______________________________________________
>> >> >>> >> pgpool-general mailing list
>> >> >>> >> pgpool-general at pgpool.net
>> >> >>> >> http://www.pgpool.net/mailman/listinfo/pgpool-general
>> >> >>> >>
>> >> >>>
>> >> > _______________________________________________
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>>
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